The use of resistant starches (RS) is of increasing importance for the food Industry. The breakdown of RS products only produces a small amount of energy for the organism. This energy supply is related solely to the oxidative breakdown of absorbed short-chain fatty acids from the large intestine. These short-chain fatty acids are end products of the carbohydrate metabolism of the intestinal microflora. Two functions are linked with the intake of RS-containing foods: provision of substrate for energy metabolism of the intestinal microflora and for that of the large intestine epithelial cells. The latter, to maintain their structure and function, are dependent on a luminal feed of short-chain fatty acids, in particular butyrate.
It has long been known that the content of highly branched amylopectin in starches, which usually consist of amylose and amylopectin of varying composition, can be reduced by specific enzymatic treatment, as a result of which the content of short-chain amylose structures can be increased (U.S. Pat. No. 3,729,380). It is also known that such products have a greater tendency to retrogradation than native starches. In this process, xcex1-amylase-resistant starch structures develop. Resistant starches (RS) are carbohydrate polymers which are not broken down by xcex1-amylase. As a result they are a reduced-energy component providing body in food compositions, within the meaning of a dietary fiber. For technical reasons, the treatment with debranching enzymes usually takes place in a not-too-concentrated aqueous starch gel.
EP 0 564 893 A1 describes and claims a process for producing an RS product which contains up to 15% RS. This process is characterized in that the aqueous suspension of a starch which contains at least 40% amylose is gelatinized and enzymatically debranched by treatment with an enzyme which opens the xcex1-1,6-glycosidic bonds, and the resultant intermediate product is then retrograded. According to EP 0 564 893 A1, the optimum starch concentration in the suspension is 15% and the examples of this EP patent application illustrate the process when the starch concentrations are either reduced to 14% or increased to 17%. The starting material contains at least 40% amylose and Is a corn starch. It is further shown that at an amylose content of 25%, no resistant starch (RS) is formed by this process. In addition, it was found that when the amylose content is increased above 40% to up to 100%, a product can be generated which contains up to 50.3% RS.
EP 0 688 872 A1 describes and claims a process for producing an RS-containing product which contains from 25 to 50% by weight of RS. According to the specifications, EP 0 688 872 A1 describes and claims a process for producing an RS-containing product in which an aqueous suspension of a partially degraded gelatinized starch is enzymatically debranched and the intermediate product is retrograded.
(In this context, xe2x80x9cpartially degraded starchxe2x80x9d is taken to mean a polymer whose molecular weight has been decreased by suitable treatment, the shortening of the chain length affecting both the amylose and the amylopectin. The degradation includes not only hydrolytic processes (acid- or enzyme-catalyzed) but also extrusion, oxidation or pyrolysis).
Acid-degraded root or tuber starches and maltodextrins of root or tuber starches are particularly emphasized. Maltodextrins are characterized by a DE value (DE: dextrose equivalent) in the range from 1 to 19.
They are produced from potato starch or tapioca starch which contain up to 25% amylose, The aqueous suspension of such maltodextrins has a solids content of 20% by weight or more for the process. The maltodextrins are further characterized in that they have high contents of oligomers having degrees of polymerization less than 10 (DP less than 10) of up to 22% by weight and a mean molecular weight of 1.3680xc3x97104 g/mol. The debranching enzymes which are used for the known process are pullulanase and isoamylase. At the end of the enzymatic treatment, retrogradation in a temperature range from 0 to 30xc2x0 C. is carried out in a time period of from 1 to 3 days, by allowing the aqueous reaction product to stand. The product is then dried by spray-drying. A pulverulent product having an RS content up to a maximum of 60% by weight is produced.
The inventive description serves the purpose of producing economically carbohydrate polymers having a high content of resistant, relatively thermally stable structures in order to be able to use them in food manufacture.
Thus one embodiment of the invention relates to xcex1-amylase-resistant polysaccharides which are poly(1,4-xcex1-D-glucans), characterized in that they have an RS content of at least 65% by weight.
In connection with the present invention, an RS content is taken to mean the content of xcex1-amylase-resistant polysaccharides, as can be determined by the method of Englyst et al. (Classification and measurement of nutritionally important starch Fractions, European Journal of Clinical Nutrition, 46 (Suppl. 23) (1992) 33-50); see also example 3.
The inventive xcex1-amylase-resistant polysaccharides can be characterized by an RS content of at least 75, and in particular at least 95% by weight.
In addition, the inventive xcex1-amylase-resistant polysaccharides can be characterized in that the poly(1,4-xcex1-D-glucans) are chemically modified in a manner known per se.
Thus, the poly(1,4-xcex1-D-glucans) can have been chemically modified by etherification or esterification in the 2, 3 or 6 position. Those skilled in the art have long been familiar with chemical modification; see, for example, the following references:
1. Functional Properties of Food Components, 2nd edition, Y. Pomeranz, Academic Press (1991)
2. Lehrbuch der Lebensmittelchemie [Textbook of food chemistry], Belitz and Grosch, Springer Verlag (1992)
3. Citrat Starch Possible Application as Resistent Starch in Different Food Systems, B. Wepner et al., European Air Concerted Action, Abstract: air3 ct94-2203, Functional Properties of Non-digestible Carbohydrates, Pro Fibre Symposium, Lisbon, February 1998, page 59.
In addition, the inventive xcex1-amylase-resistant polysaccharides can be characterized in that they have a degree of branching in the 6 position of at most 0.5%.
In addition, the inventive xcex1-amylase-resistant polysaccharides can be characterized in that they have a degree of branching In the 2 and/or 3 position of, in each case, at most 1.0%, and in particular at most 0.5%.
In addition, the xcex1-amylase-resistant polysaccharides can be characterized in that the poly(1,4xcex1-D-glucans) have a molecular weight of from 0.75xc3x97102 to 107, preferably from 103 to 106, and preferably from 103 to 5xc3x97105 g/mol and/or are water-insoluble.
In addition, the inventive xcex1-amylase-resistant polysaccharides can be characterized in that the poly(1,4-xcex1-D-glucans) have neither been debranched, in particular have neither been enzymatically debranched, nor have been reduced with respect to their chain length (and thus with respect to their molecular weight), in particular not by enzyme catalysis, acid catalysis, extrusion, oxidation or pyrolysis.
In addition, the inventive xcex1-amylase-resistant polysacchardes can be obtainable by a process comprising the following steps:
a) producing a suspension or dispersion from water-insoluble poly(1,4-xcex1-D-glucans) and water;
b) warming the suspension or dispersion;
c) cooling the resultant gel and retrogradation of the gel at a temperature which is lower than the temperature of the heated gel; and
d) if appropriate drying the resultant product.